The contributions of modern physics have increased the availability of radioactive x-ray and gamma-ray emitting materials in industry and nuclear medicine. As radioactive emission principally occurs outside of the visible part of the electromagnetic spectrum, an unaided human observer is unable to "see" a source of radioactive emission. It is difficult, therefore, to distinguish a source of x-ray and gamma ray emission from non-emitting neighboring and visually similar objects. Various techniques exist to locate a source of radioactive emission. One technique requires trial and error search with a Geiger counter. Another technique uses a scintillation detector. The information provided by these techniques is limited to the intensity and location of radioactive emission, and reveals nothing about the shape of a radioactive object or the distribution of radioactivity within the object. An x-ray camera formed by placing x-ray sensitive film behind a pinhole in an x-ray shield merely provides a recording of a two-dimensional facsimile of an x-ray or gamma-ray emitting object in one perspective. The facsimile can be viewed only after a delay for processing of the film. Furthermore, a single pinhole aperture camera is rendered extremely inefficient by the minute aperture of the pinhole.
Other, existing x-ray or gamma-ray cameras employ either parallel or converging collimators to bring an essentially parallel beam projection of a radioactive object onto a detector. The detector may be in the nature of a film, a scintillator, or a phosphor material which converts x-rays and gamma-rays into visible light. The visible light generated, together with positional information, is then processed by any of a wide variety of methods using such devices as photomultiplier tubes (e.g., Anger cameras), image intensifiers, visible light cameras, video cameras, and centroid-computing electronics in various combinations. Without the additional steps of making successive exposures and subsequent reconstructions, a particular object-to-camera geometry provides only a two-dimensional single perspective image of an x-ray or gamma-ray emitting object. Although a steroscopic pair of such cameras may be used to obtain a stereoscopic pair of images which, upon reconstruction, provide a stereoscopic view of a single perspective of an object, that view lacks full horizontal and vertical parallax.
An earlier invention, a low intensity x-ray image scope ("Lixiscope") disclosed in U.S. Pat. No. 4,142,101, is a fully portable, hand-held device which provides an intensified visible-light image of objects illuminated with point sources of x-rays or gamma rays. It uses an x-ray to visible-light converter to drive a visible-light image intensifier having one or more microchannel plate electron multipliers. The Lixiscope provides a viewer with a visible shadow, in real time, of the illuminated objects.